1. Field of the Invention
The present invention relates generally to methods and systems for production of hydrocarbons, hydrogen, and/or other products from various subsurface formations such as hydrocarbon containing formations.
2. Description of Related Art
Hydrocarbons obtained from subterranean formations are often used as energy resources, as feedstocks, and as consumer products. Concerns over depletion of available hydrocarbon resources and concerns over declining overall quality of produced hydrocarbons have led to development of processes for more efficient recovery, processing and/or use of available hydrocarbon resources. In situ processes may be used to remove hydrocarbon materials from subterranean formations that were previously inaccessible and/or too expensive to extract using available methods. Chemical and/or physical properties of hydrocarbon material in a subterranean formation may need to be changed to allow hydrocarbon material to be more easily removed from the subterranean formation and/or increase the value of the hydrocarbon material. The chemical and physical changes may include in situ reactions that produce removable fluids, composition changes, solubility changes, density changes, phase changes, and/or viscosity changes of the hydrocarbon material in the formation.
Large deposits of heavy hydrocarbons (heavy oil and/or tar) contained in relatively permeable formations (for example, in tar sands) are found in North America, South America, Africa, and Asia. Tar can be surface-mined and upgraded to lighter hydrocarbons such as crude oil, naphtha, kerosene, and/or gas oil. Surface milling processes may further separate the bitumen from sand. The separated bitumen may be converted to light hydrocarbons using conventional refinery methods. Mining and upgrading tar sand is usually substantially more expensive than producing lighter hydrocarbons from conventional oil reservoirs.
In situ production of hydrocarbons from tar sand may be accomplished by heating and/or injecting fluids into the formation. U.S. Pat. No. 4,084,637 to Todd; U.S. Pat. No. 4,926,941 to Glandt et al.; U.S. Pat. No. 5,046,559 to Glandt, and U.S. Pat. No. 5,060,726 to Glandt, each of which are incorporated herein by reference, describe methods of producing viscous materials from subterranean formations that includes passing electrical current through the subterranean formation. Steam may be injected from the injector well into the formation to produce hydrocarbons.
Oil shale formations may be heated and/or retorted in situ to increase permeability in the formation and/or to convert the kerogen to hydrocarbons having an API gravity greater than 10°. In conventional processing of oil shale formations, portions of the oil shale formation containing kerogen are generally heated to temperatures above 370° C. to form low molecular weight hydrocarbons, carbon oxides, and/or molecular hydrogen. Some processes to produce bitumen from oil shale formations include heating the oil shale to a temperature above the natural temperature of the oil shale until some of the organic components of the oil shale are converted to bitumen and/or fluidizable material.
U.S. Pat. No. 3,515,213 to Prats, which is incorporated by reference herein, describes circulation of a fluid heated at a moderate temperature from one point within the formation to another for a relatively long period of time until a significant proportion of the organic components contained in the oil shale formation are converted to oil shale derived fluidizable materials.
U.S. Pat. No. 3,882,941 to Pelofsky, which is incorporate by reference herein, describes recovering hydrocarbons from oil shale deposits by introducing hot fluids into the deposits through wells and then shutting in the wells to allow kerogen in the deposits to be converted to bitumen which is then recovered through the wells after an extended period of soaking.
U.S. Pat. No. 7,011,154 to Maher et al., which is incorporated herein by reference herein, describes in situ treatment of a kerogen and liquid hydrocarbon containing formation using heat sources to produce pyrolyzed hydrocarbons. Maher also describes an in situ treatment of a kerogen and liquid hydrocarbon containing formation using a heat transfer fluid such as steam. In an embodiment, a method of treating a kerogen and liquid hydrocarbon containing formation may include injecting a heat transfer fluid into a formation. Heat from the heat transfer fluid may transfer to a selected section of the formation. The heat from the heat transfer fluid may pyrolyze a substantial portion of the hydrocarbons within the selected section of the formation. The produced gas mixture may include hydrocarbons with an average API gravity greater than about 25°.
As discussed above, there has been a significant amount of effort to produce hydrocarbons and/or bitumen from oil shale. At present, however, there are still many hydrocarbon containing formations that cannot be economically produced. Thus, there is a need for improved methods for heating of a hydrocarbon containing formation and production of hydrocarbons having desired characteristics from the hydrocarbon containing formation are needed.